With the recent increase in concern about environmental issues, the demand on automobiles for better fuel economy is increasing. Better fuel economy is also being required of rubber compositions used for automotive tires. For example, rubber compositions containing a conjugated diene polymer (e.g. polybutadiene, butadiene-styrene copolymer) and a filler (e.g. carbon black, silica) are used for automotive tires.
Patent Literature 1 proposes a method for improving fuel economy; this method uses a diene rubber (modified rubber) that is modified by an organosilicon compound containing an amino group and an alkoxy group. The use of such a modified rubber improves fuel economy; however, it tends to increase Mooney viscosity so that processability can be deteriorated. Moreover, rubber compositions for automotive tires also need to have tensile strength at break, for example. As tensile strength at break is usually incompatible with fuel economy, balanced improvements in these properties are difficult to achieve at high levels.